Inflatable support

ABSTRACT

An alternating pad comprises a first set and a second set of alternately inflatable cells. Both sets of inflatable cells are supplied with air from a pump via a rotary valve. A sensor is positioned under the pad to receive pressure exerted by a patient upon movement and to be compressible relative to the applied pressure. Any change in patient position or movement will cause an alteration in the airflow in the sensor pad tube and will reduce or increase the differential pressure measured at the pressure transducer. Based on this feedback the microprocessor directly controls the power level to the pump and increases or decreases the air flow to the cells to alter the amplitude of the cells and also controls the timing of the rotary valve to change the timing of the inflation and deflation cycle.

This invention relates to an inflatable support, in particular aninflatable support that measures the movements of a patient supported onthe support and adjusts the support provided depending on the movementsdetected.

There have been several techniques developed to measure body movement,patient entry and patient exit from a support using fluctuations in airpressure in the inflatable supports or inflatable bodies insertedbetween the patient and a supporting surface. The technique of measuringbody movements by recording the air pressure in an air filled pad placedunder a mattress was described by Kusunoki (1985). Another system hasbeen developed to measure the respiratory movements of subjects bymeasuring pressure changes in a supporting air mattress (Hernandez1995). U.S. Pat. No. 6,036,660 describes a system that uses transducersto detect and display movement in an air-filled cell or cells between apatient and a support.

Overall, these systems give a numerical or visual display of detectedmovement using the fluctuation of static air in an enclosed cell orcells. Since, there is a link between the rate of spontaneous bodymovements and the risk of developing pressure sores (Exton-Smith et al,1961), the information provided or displayed helps in the assessment ofthe risk of pressure sore development. The information can be used toincrease the manual turning of the patient or to aid the decision tomove the patient to another support surface. Equally, the informationcan be completely ignored in a busy ward.

The aim of this invention is to provide an inflatable support whoseinflation and/or deflation regime is automatically controlled independence upon the movement of a patient on the support thereforepatient comfort and pressure relief is automatically optimised withoutrequiring external input from a carer or nurse.

Accordingly, the invention provides an inflatable support supplied withair from a pump by means of valve, a sensor positioned under the supportto measure the movements of a patient on the support, and control meansadjusting the inflation and/or deflation of the support by the pump inresponse to the measurement values from the sensor. Thus, where apatient is able to move by themselves on a regular basis on aninflatable mattress, the pressures at which the mattress is inflated canbe adjusted to improve comfort without increasing the risk of pressuresore development.

In an alternating pressure mattress, it is known that there is acompromise between an effective alternating pressure cycle used toreduce the risk of pressure sore development and the comfort experiencedby the patient. Preferably, the inflatable support is an alternatinginflatable support and more preferably, the control means adjusts theinflation and/or deflation pressures and cycle times of the support inresponse to the measurement values from the sensor.

Therefore, where a patient is able to move by themselves on a regularbasis on an alternating mattress, the inflation/deflation cycleparameters can be altered to improve comfort without increasing the riskof pressure sore development. For example, the present invention canlengthen the cycle time to provide extra comfort for those patients whoare making significant autonomous movements, or shorten the time forthose patients that require more active pressure relief.

Preferably, a display of the patient movement is also provided. Many ofthe risk assessment tools (Waterlow, Norton & Braden) use movement aspart of their scoring system and an accurate movement display would helpthe nurses select the correct support surface.

An embodiment of the present invention is described below, by way ofexample only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a support according to the invention;

FIG. 2 is a flow chart showing the control algorithm; and

FIGS. 3 a and 3 b show displays of the various body movements measuredaccording to the invention.

Referring to FIG. 1, an alternating pad 1 is shown comprising a firstset 11 and a second set 12 of alternately inflatable cells. Both sets ofinflatable cells are supplied with air from a pump 6 via a rotary valve7. A pair of air supply lines 14 lead from the rotary valve 7 to the pad1.

A tube 10 of a sensor 8 is connected at one end to the output of thepump 6 and at the other end to a solenoid 44, pressure transducer 16 anda restrictor 15. The sensor 8 is positioned under the pad 1 to receivepressure exerted by a patient upon movement and to be compressiblerelative to the applied pressure.

In use, the pump 6 delivers air to the pad 1 by means of a rotary valve7 so that each set of cells of the pad is alternately inflated anddeflated. A pressure transducer 5 is used to check the pressure of theoutput from the pump 6. The system operates on an inflation/deflationcycle repeating over periods varying from two minutes to over twentyminutes.

During the inflation cycle, the rotary valve 7 is in such a positionthat a portion of the flow goes via the tube 10 and the rest fills thecells 11 or 12 depending on the cycle. Any change in patient position ormovement will cause an alteration in the airflow in the sensor pad tube10 and will reduce or increase the differential pressure measured at thepressure transducer 16. Based on this feedback the microprocessordirectly controls the power level to the pump and therefore thecompressor(s) pneumatic output, thus increasing or decreasing the airflow to the cells 11, 12 to alter the amplitude of the cells 11, 12 andcontrol the timing of the rotary valve 7 to change the timing of theinflation and deflation cycle.

The sensor air flow is measured via the differential pressure across therestrictors 15. The differential pressure is measured by pressuretransducer 16 by comparison to atmospheric pressure.

The pressure recordings at the sensor exit, because of fluctuations inthe air within the sensor 8, are measured and the movements analysed,the control means then controls the rotary valve 7, and thus the timingof the pressure cycle in response to the movements detected. Preferably,the detected movement values are also displayed on a display panel onthe pump.

As shown in FIGS. 3 a and 3 b, the pressure transducer 16 recordings candistinguish between the various types of movements, including large andsmall body movements, patient exit and patient location. A windowingtechnique is used to detect the various movement parameters.

The large body movements indicate a significant change in body positionwith a subsequent redistribution of body weight. If the large bodymovements are within normal levels, for example, 1 large movement every10 minutes, then the frequency of the flow cycle is reduced, increasingthe comfort to the patient. The frequency is increased when there are nolarge body movements detected.

The patient exit is detected by sudden large changes in the pressure, orby comparison of the pressures between consecutive cycles.

Additionally, the pad 1 can be segmented into zones for a heel section,an upper leg section, a mid torso section, and a head section. Thesections can be inflated at differing amplitudes for comfort and reducedrisk of pressure sore development.

Although the particular embodiment described above relates to analternating pressure pad 1, the invention applies equally to a staticpressure pad with a sensor and further a pad having a zoned head, upperleg, torso and heel sections.

The pump 6 uses powered pulse width modulated (PWM) driven compressorsas opposed to the mains alternating current driven compressors of theprior art. A micro-controller creates the driving waveform for thecompressors C1, C2 with variable mark space constant repetition rate andconstant amplitude, so that the pump 6 is not dependent for performanceon any particular mains voltage or frequency. Therefore, the pump 6 canbe operated from the mains voltage of any country. The compressorsoutput is varied by varying the PWM mark space ratio from zero tomaximum.

The sensor 8 and control means can be used to display the number oftimes the patient has moved on the support and sound an alarm if thepatient has not moved or initiate contact with a third party by means ofconventional communications devices.

1. An inflatable support comprising: a pad effective to receive air froma pump by means of a valve, a sensor positioned under the pad effectiveto measure the movements of a patient on the pad to produce measurementvalves, and control means effective to automatically adjust theinflation and/or deflation of the pad by the pump in response to themeasurement values.
 2. An inflatable support as claimed in claim 1wherein the pad is an alternating pressure pad.
 3. An inflatable supportas claimed in claim 2 wherein the control means adjusts the inflationand/or deflation of the support by the pump and further controls thevalve to adjust cycle times of the inflation and/or deflation inresponse to the measurement values.
 4. An inflatable support as claimedin claim 1, further comprising a display effective to display arepresentation of the measurement valves.
 5. The inflatable support asrecited in claim 1, wherein during the inflation, the valve allows atleast part of the air to go to the sensor; the movements of the patientproduce a change in the air in the sensor; and the movement values areproduced based on the change in the air in the sensor.
 6. The inflatablesupport as recited in claim 1, wherein the sensor comprises a pressuretransducer.
 7. The inflatable support as recited in claim 1, wherein thepad is segmented into zones for a heel section, an upper leg section, amid torso section and a head section.